The present invention relates to a liquid filter arrangement in accordance with the preamble to patent claim 1.
The purpose of a liquid filter is to separate contaminating particles from a liquid which is to be used in one way or another in equipment to which the liquid is fed and whose operation may be disturbed or prevented if such particles accompanying the liquid enter the equipment concerned. The liquid may for example be fuel for combustion in an engine, hydraulic oil for operating or driving hydraulic equipment, or liquid intended to be finely divided by means of a spray nozzle.
In cases where the liquid filter is a fuel filter for a gasoline engine, it is usually incorporated between a fuel pump and the engine""s carburetor/injection arrangement. In cases where the engine is a diesel engine, the fuel filter is usually incorporated between a feed pump and the engine""s injection pump.
The interchangeable filter insert (filter cartridge) in such a fuel filter may for example consist of a prismatic or circularly cylindrical stack of felt pads or filter paper discs. In cases where a paper filter insert is used, it may for example consist of a special water-repellent paper filter element folded in a spiral configuration in order to form pockets, pores or cells resulting in maximum filtration surface for a given area/volume.
The efficiency of such an initially very effective filter insert will nevertheless inevitably decrease gradually as the particle-intercepting pockets/pores/cells become increasingly choked with separated particles. The filter insert has therefore eventually to be replaced by a completely new filter insert.
On the occasion of such changing of a filter insert or a filter element in a fuel filter, it is difficult to avoid fuel spillage if the filter housing is full of fuel which is under a certain positive pressure. In such cases, fuel will escape from the filter housing when the lid of the housing is unscrewed, thereby reducing the pressure in the fuel filter. Even if quite a large proportion of the fuel in the filter housing escapes when the housing lid is removed, a certain quantity of fuel will still remain in the filter housing when the old filter insert (filter element) has been-removed from the filter housing.
The insertion of a new filter element into the filter housing does require, however, the filter housing to be at least nearly empty of fuel, since there would otherwise be risk that fuel remaining in the housing might be forced out of the filter housing by the insertion of the new filter element into the housing.
The object of the present invention is to avoid the aforesaid fuel spillage problem by providing a new type of liquid filter arrangement which prevents fuel being forced out of the filter housing when the housing lid is removed, and which eliminates any risk of fuel being forced out of the filter housing by the insertion of a new filter element into the housing.
The aforesaid object is achieved, in a liquid filter arrangement describe below.
Primary distinguishing aspects of the invention are therefore that the liquid chamber incorporates a central tube which is concentric with the central longitudinal axis of the filter housing and which has its lower end fastened in the central bottom portion of the filter housing, and that there is arranged about the central tube a sleeve-like filter element which is provided at the bottom with an annular end piece sealingly surrounding the central tube and is provided at the top with an end disc by which the filter element is connected to a lid fastened sealingly into the upper part of the filter housing. When the filter element is in its fitted position, the end piece blocks the inlet to a draining duct in the central tube, which duct leads to a draining outlet from the chamber. The inlet to the draining duct is so positioned relative to the end piece and the lid that as the filter element is taken out of the chamber the duct inlet is freed and opened before the sealing effect between the lid and the filter housing ceases. The seals between the lid and the filter housing are thus arranged at a level which is higher than the highest liquid level in the chamber when the sealing effect ceases.
The aforesaid fuel spillage problem is therefore avoided on the occasion of filter element changing because of the presence of the draining duct in the lower part of the central tube, which duct is opened so that residual fuel in the liquid chamber can escape from the chamber before the pressure-maintaining sealing effect between the lid and the filter housing ceases. The liquid thus tapped from the chamber via the draining duct is advantageously led from the draining outlet back to the ordinary liquid tank during the changing of the filter element.
The end piece of the filter element preferably also includes not only a sleeve portion which sealingly surrounds the central tube and which has a lower end adjacent to the bottom of the liquid chamber, but also a disc-shaped flange portion which protrudes radially, perpendicular to the central tube, from the upper end of the sleeve portion. The end disc of the filter element may advantageously be a planar circular disc situated in an imaginary plane perpendicular to the central tube. The end disc is preferably connected to the lid of the filter housing by a snap connection which keeps the filter element stationary relative to the lid.
The filter cartridge (filter insert) consisting of the filter element with associated end piece and end disc can therefore be disassembled as a single unit from the liquid chamber by removing the lid from the filter housing, which involves the filter element snap-fastened into the lid via the end disc accompanying the lid upwards when the latter is released and disassembled from the filter housing.
Tightness between the end piece and the outside of the central tube may with advantage be provided by a pair of annular seals, e.g. O-rings, acting between the outside of the central tube and the inside of the sleeve portion surrounding the end piece. These two axially separated annular seals are preferably placed in a pair of parallel circumferential grooves in the inside of the sleeve portion. When the filter element is in its fitted position whereby the lower end of the sleeve portion is adjacent to the bottom of the liquid chamber, the two annular seals are situated on axially opposite sides of the orifice to the inlet of the draining duct. In alternative embodiments of the invention, tightness may be provided by a seal specially designed for the purpose, instead of the two O-rings. In other alternative embodiments it is also possible for these seals to be fitted to the central tube instead of to the sleeve portion.
The mutually cooperating sealing surfaces of the lid and the upper end section of the filter housing may advantageously include the lid having a cylindrical outer shell surface that forms a sealing surface and cooperates with a corresponding annular sealing surface on an internal portion of the upper end section of the filter housing. In such cases the lid""s shell surface acting as sealing surface is advantageously provided with a circumferential seal. For example, that seal may be an O-ring provided in a circumferential groove in the shell surface to bear upon the sealing surface on the upper end section of the filter housing.
The lid is preferably fastened by screwing into the upper section of the filter housing, which entails the lid and the upper end section of the filter housing being provided with mutually cooperating and engaging threaded portions according to claim 10.
When filter element changing is to take place, the lid can therefore be screwed upwards out of the upper end section of the filter housing, which means that the lid is accompanied by the filter element fastened into it via the end disc and that the filter element""s seals situated in the end piece free and open the draining channel inlet in the central tube before the seal acting between the sealing surfaces of the lid and of the upper end section of the filter housing moves so far that their sealing effect ceases. To ensure this two-stage deactivation of the respective seals of the draining channel inlet and the lid, the liquid filter arrangement may have the axial distance (h) between the seal, which is situated on the sleeve portion of the end piece and which is close to the bottom of the liquid chamber, and the orifice to the inlet of the draining duct be less than the distance H between the seal on the lid shell surface and the axially outermost edge of the corresponding sealing surface on the upper end of the filter housing, so that the drainage channel is opened for drainage before the lid and filter move free of the filter housing.
It may quite generally be observed that a liquid filter arrangement according to the present invention affords a number of advantages relative to known liquid filter arrangements. For example, liquid spillage (e.g. fuel spillage) can be avoided when changing filter elements, since necessary draining of residual liquid (e.g. fuel) in the filter housing is assured before the filter element change can take place. Further advantages of an arrangement according to the invention include the fact that the draining duct can be accommodated in the central tube, which is in practice brought about at the stage of casting the central tube in cases where the latter is made by casting. The constructional configuration of the liquid filter arrangement according to the invention makes it easy and inexpensive to manufacture and means that satisfactory draining function can be assured, inter alia because the arrangement consists of a small number of constituent elements which need not be made with particularly high precision of manufacture, partly because necessary seals in the liquid filter arrangement can be provided by separate sealing elements such as O-rings.